Swimming pools, hot tubs and spas, as well as other water systems, are subject to contamination from microbes, e.g., algae and fungus, causing unwanted discoloration and turbidity in the water system. Typical organisms that will grow in the water in such systems include Chlorococcum, Chlorella, Cledaphora, Microcystis, Oscilratoris, Spirosyra, Olaothrisx, Vanetteria, and Aspergilles flavus. The prevention or inhibition of growth of these microorganisms in water systems has been a problem.
It is customary to treat water systems with one or more sanitizers and/or sanitizer/oxidizer combinations to control the growth of microorganisms. The sanitizers most commonly used to control the growth of microorganisms are chemicals that generate hypochlorite or hypobromite species when dissolved in water. There are many hypochlorite generating chemicals, with the more common ones being chlorine gas, alkali metal hypochlorites such as sodium hypochlorite, alkaline earth metal hypochlorites such as calcium hypochlorite and lithium hypochlorite, halogenated hydantoins and chlorinated isocyanuric acid derivatives such as sodium or potassium dichloro-s-triazinetrione.
Although the foregoing halogen species are excellent water treatment agents, it can be difficult to maintain an efficient level of the halogens to control the growth of the microorganisms. This is especially true for bromine systems and unstabilized chlorine systems. Thus, it is necessary with these systems to continuously replace the lost halogens. With this type of treatment program, there frequently are periods of unnecessarily high halogen levels which are wasteful of the chemicals, and of low to no halogen levels which invite the growth of microorganisms.
Hydrogen peroxide and other inorganic peroxygen compounds, in particular persulfates and persulfuric acids and their salts, are known to be active oxygen containing compounds which are also used for oxidation of water systems. However, hypochlorite compounds and active oxygen compounds generally are not used together to treat water systems. In fact, the manufacturers of both chlorine compounds and peroxygen compounds, as well as other literature sources, have recommended against the blending of these compounds due to their chemical incompatibilities which may lead to explosions or fire.
Also, the Encyclopedia of Chemical Technology (Kirk-Othmer), volume 17, page 1, reports that hydrolysis to H.sub.2 O.sub.2 followed by the disproportionation of H.sub.2 O.sub.2 is the main path for decomposition of inorganic peroxide, e.g., EQU K.sub.2 S.sub.2 O.sub.8 +2 H.sub.2 O.fwdarw.2 KHSO.sub.4 +H.sub.2 O.sub.2
Inorganic peroxides neutralize chlorine in water by acting as dechlorinating agents: EQU HOCl+H.sub.2 O.sub.2 .fwdarw.O.sub.2 (Ag)+H.sup.+ +Cl.sup.- +H.sub.2 O
Based on the preceding information, it would appear that a combination of these types of compounds would be impractical.
The separate addition of chlorine compounds and a peroxy compound as oxidizing agents is taught in U.S. Pat. No. 3,702,298 issued November 1972 to F. J. Zsoldos et al. This patent teaches the addition of peroxy compounds to swimming pool water containing multivalent metals such as Ag and Cu to raise the valence of the metals to a level at which the metals provide an oxidizing action. Chlorine may also be present as disinfectant in the water system. However, it has not been suggested that chlorine source materials be physically combined with the peroxy compounds in the same dry composition.
In U.S. Pat. No. 4,780,216, issued Oct. 25, 1988 to John A. Wojtowicz, there are disclosed calcium hypochlorite sanitizing compositions consisting essentially of a mixture of calcium hypochlorite and a peroxydisulfate comound. The compositions are indicated to be useful in sanitizing water while helping to minimize the increase in the pH of the water.
In U.S. Pat. No. 4,594,091, issued Jun. 10, 1986 to John W. Girvan, a method of controlling algal and fungal growth using sodium tetraborate or potassium tetraborate in water systems is disclosed. The Girvan patent teaches a method of adding from 10 to 500 ppm boron to water systems. Girvan teaches the separate addition of the boron material, particularly sodium tetraborate, to a water system, which may also include a sanitizer. The results achieved with this approach vary greatly from one swimming pool to the next.
The use of calcium hypochlorite mixed with water-soluble, hydrated inorganic salts to provide a composition which is resistant to exothermic, self-propagating decomposition is disclosed in U.S. Pat. No. 3,793,216, issued to Dychdala et al. on Feb. 19, 1974. The inorganic salts are selected from various hydrated alkali metal and alkaline earth metal phosphates, silicates, borates, carbonates and sulfates.
It has also been known in the prior art to combine boric acid and trichloro-s-triazinetrione. This combination has been described by industry practice for the purpose of increasing solubility and reducing overall raw material costs.
The present invention is surprising in its divergence from teachings of the prior art. For example, the prior art has included indications that boron materials would not be efficacious at the levels utilized herein. See, e.g., Marshall and Hrenoff, Journal of Infectious Diseases, vol. 61, p. 42 (1937).
The prior art systems for the treatment of water for controlling growth of antimicrobials have generally had difficulties with providing consistently dependable results. Theoretical approaches have had shortcomings in practice because of the need for careful attention to water chemistries. The best of systems are inadequate if they are too difficult to be used in practice. The present system and compositions address this problem by providing a simple, reliable and consistent system for the treatment of water systems.